Clinical Translational Core: Abstract The mission of the Translational Clinical Core of the UCLA IDDRC, established in 2015, is to support high quality, multidisciplinary, collaborative clinical translational research advancing knowledge of causes, prevention, diagnosis, and treatment of intellectual and developmental disabilities (IDDs). To accomplish this, the Core will provide research consultation; access to reduced cost, specialized, research quality diagnostic and phenotypic assessments; recruitment support; training; data management; and other aids for IDDRC investigators bridging clinical research with basic science. The Core is engaged in advancing assessment methods for IDD research through innovative measure development, evaluation, and dissemination. The Core also supports outreach, biospecimen banking, and data management. In addition, the Core will participate in IDDRC Network and other IDDRC-related multi-site clinical investigations. Over the past 4 years, the Core has successfully established effective procedures for support of ongoing and new clinical IDD studies, nearly doubling the number supported during that timeframe, and has contributed new phenotyping measurements to the field. The Core has been impactful in supporting several new studies by early career investigators new to clinical studies. In this renewal, we are strengthening the Core by adding two new Core Co-Investigators (Drs. Catherine Lord and Rujuta Bhatt Wilson) who bring special expertise in social, diagnostic, behavioral, motor, and neurological assessments, IDD intervention trials, longitudinal studies, and large-scale training on gold standard diagnostic instruments. Core support is leveraged to achieve substantial cost efficiency, reducing individual project costs and by removing burdens of training, quality control, and maintenance of reliability from individual studies. Core access then enables expansion of research efforts and enhances quality of UCLA IDDRC research by establishing uniformity in diagnosis, phenotyping, and conduct of clinical studies. Measurement development efforts, utilizing sophisticated analytics such as Item Response Theory and machine learning, are aimed at addressing methodologic gaps that have plagued prior clinical research efforts relating to IDDs, and foster new research by providing tools better suited to capturing clinical manifestations of underlying biology, hence advancing clinical translation. Our training aims to build capacity for IDD research. Our team is especially well suited for advancing assessment approaches for use in minimally verbal individuals, and very young children at risk for IDDs, a strength of our team. Core investigators are well known for measurement and paradigm development, lifespan studies, and studies of higher functioning subjects across a range of IDDs.